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perf/core: Fix exclusive events' grouping

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So far, we tried to disallow grouping exclusive events for the fear of
complications they would cause with moving between contexts. Specifically,
moving a software group to a hardware context would violate the exclusivity
rules if both groups contain matching exclusive events.

This attempt was, however, unsuccessful: the check that we have in the
perf_event_open() syscall is both wrong (looks at wrong PMU) and
insufficient (group leader may still be exclusive), as can be illustrated
by running:

  $ perf record -e '{intel_pt//,cycles}' uname
  $ perf record -e '{cycles,intel_pt//}' uname

ultimately successfully.

Furthermore, we are completely free to trigger the exclusivity violation
by:

   perf -e '{cycles,intel_pt//}' -e '{intel_pt//,instructions}'

even though the helpful perf record will not allow that, the ABI will.

The warning later in the perf_event_open() path will also not trigger, because
it's also wrong.

Fix all this by validating the original group before moving, getting rid
of broken safeguards and placing a useful one to perf_install_in_context().

Signed-off-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: <stable@vger.kernel.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vince Weaver <vincent.weaver@maine.edu>
Cc: mathieu.poirier@linaro.org
Cc: will.deacon@arm.com
Fixes: bed5b25ad9 ("perf: Add a pmu capability for "exclusive" events")
Link: https://lkml.kernel.org/r/20190701110755.24646-1-alexander.shishkin@linux.intel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Alexander Shishkin 2019-07-01 14:07:55 +03:00 committed by Ingo Molnar
parent 2f217d58a8
commit 8a58ddae23
2 changed files with 27 additions and 12 deletions
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5
include/linux/perf_event.h
View File

@ -1055,6 +1055,11 @@ static inline int in_software_context(struct perf_event *event)
return event->ctx->pmu->task_ctx_nr == perf_sw_context;
}
static inline int is_exclusive_pmu(struct pmu *pmu)
{
return pmu->capabilities & PERF_PMU_CAP_EXCLUSIVE;
}
extern struct static_key perf_swevent_enabled[PERF_COUNT_SW_MAX];
extern void ___perf_sw_event(u32, u64, struct pt_regs *, u64);

34
kernel/events/core.c
View File

@ -2553,6 +2553,9 @@ static int __perf_install_in_context(void *info)
return ret;
}
static bool exclusive_event_installable(struct perf_event *event,
struct perf_event_context *ctx);
/*
* Attach a performance event to a context.
*
@ -2567,6 +2570,8 @@ perf_install_in_context(struct perf_event_context *ctx,
lockdep_assert_held(&ctx->mutex);
WARN_ON_ONCE(!exclusive_event_installable(event, ctx));
if (event->cpu != -1)
event->cpu = cpu;
@ -4360,7 +4365,7 @@ static int exclusive_event_init(struct perf_event *event)
{
struct pmu *pmu = event->pmu;
if (!(pmu->capabilities & PERF_PMU_CAP_EXCLUSIVE))
if (!is_exclusive_pmu(pmu))
return 0;
/*
@ -4391,7 +4396,7 @@ static void exclusive_event_destroy(struct perf_event *event)
{
struct pmu *pmu = event->pmu;
if (!(pmu->capabilities & PERF_PMU_CAP_EXCLUSIVE))
if (!is_exclusive_pmu(pmu))
return;
/* see comment in exclusive_event_init() */
@ -4411,14 +4416,15 @@ static bool exclusive_event_match(struct perf_event *e1, struct perf_event *e2)
return false;
}
/* Called under the same ctx::mutex as perf_install_in_context() */
static bool exclusive_event_installable(struct perf_event *event,
struct perf_event_context *ctx)
{
struct perf_event *iter_event;
struct pmu *pmu = event->pmu;
if (!(pmu->capabilities & PERF_PMU_CAP_EXCLUSIVE))
lockdep_assert_held(&ctx->mutex);
if (!is_exclusive_pmu(pmu))
return true;
list_for_each_entry(iter_event, &ctx->event_list, event_entry) {
@ -10947,11 +10953,6 @@ SYSCALL_DEFINE5(perf_event_open,
goto err_alloc;
}
if ((pmu->capabilities & PERF_PMU_CAP_EXCLUSIVE) && group_leader) {
err = -EBUSY;
goto err_context;
}
/*
* Look up the group leader (we will attach this event to it):
*/
@ -11039,6 +11040,18 @@ SYSCALL_DEFINE5(perf_event_open,
move_group = 0;
}
}
/*
* Failure to create exclusive events returns -EBUSY.
*/
err = -EBUSY;
if (!exclusive_event_installable(group_leader, ctx))
goto err_locked;
for_each_sibling_event(sibling, group_leader) {
if (!exclusive_event_installable(sibling, ctx))
goto err_locked;
}
} else {
mutex_lock(&ctx->mutex);
}
@ -11075,9 +11088,6 @@ SYSCALL_DEFINE5(perf_event_open,
* because we need to serialize with concurrent event creation.
*/
if (!exclusive_event_installable(event, ctx)) {
/* exclusive and group stuff are assumed mutually exclusive */
WARN_ON_ONCE(move_group);
err = -EBUSY;
goto err_locked;
}